text: Lorentz force sigmometry (LOFOS) is a contactless method for measuring the thermophysical properties of materials, no matter whether it is a fluid or a solid body. The precise measurements of electrical value, density, viscosity, thermal  conductivity and surface tension of molten metals are in great importance in industry applications. One of the major problems in the experimental measurements of the thermophysical properties at high temperature (>1000 K) in the liquid  state  is  the  problem  of  chemical  reaction  between  the  hot  fluid  and  the  electrical  probes.
  The basic equation for calculating the electrical conductivity is derived from the equation that links the mass flow rate  and Lorentz force  generated by magnetic field in flow:
  <div class="center"> <math>
  \dot{m} \left(t \right) = \frac{K}{\Sigma} F \left(t \right) \quad
  where  is the specific electrical conductivity equals to the ratio of the electrical conductivity  and the  mass density of fluid .   is a calibration factor  that depends on the  geometry of the LOFOS system.
  From equation above the cumulative mass during operating time is determined as
  <div class="center"> <math>
  M=\int _{t1}^{t2} \dot{m} \left(t \right) dt = \frac{K}{\Sigma} \int _{t1}^{t2} F \left(t \right) dt = \frac{K}{\Sigma} \tilde{F} \quad ,
  where   is the integral of Lorentz force  within the time process. From this equation and considering the specific  electrical  conductivity formula, one can derive the final equation to compute the electrical conductivity for the fluid, in the form
  <div class="center"> <math>
  \sigma = \rho K \frac{\tilde{F}}{M} \quad .